Intraluminal, intracavity, intravascular, and intracardiac treatments and diagnosis of medical conditions utilizing minimally invasive procedures are effective tools in many areas of medical practice. These procedures are typically performed using imaging and treatment catheters that are inserted percutaneously into the body and into an accessible vessel of the vascular system at a site remote from the vessel or organ to be diagnosed and/or treated, such as the femoral artery. The catheter is then advanced through the vessels of the vascular system to the region of the body to be treated. The catheter may be equipped with an imaging device, typically an ultrasound imaging device, which is used to locate and diagnose a diseased portion of the body, such as a stenosed region of an artery. For example, U.S. Pat. No. 5,368,035, issued to Hamm et al., the entire disclosure of which is incorporated herein by reference, describes a catheter having an intravascular ultrasound imaging transducer.
FIGS. 1a and 1b show an example of an imaging transducer assembly 1 known in the art. The imaging transducer assembly 1 is situated within the lumen 50 of a sheath 5 of a guidewire (partially shown) and is capable of rotating 360° within the sheath 5, about the axis of the sheath 5. The lumen 50 of the sheath 5 is typically filled with a sonolucent liquid, such as water or saline that surrounds the transducer assembly 1. The imaging transducer assembly 1 includes a drive shaft 10 and a stainless steel housing 20 coupled to the distal end of the drive shaft 10, which serves to reinforce the structure of the transducer assembly 1. Toward the distal end of the housing 20 is a layer of piezoelectric crystal (“PZT”) 40, attached to an acoustic lens 30 exposed to the sonolucent liquid in the lumen 50.
During operation, the imaging transducer assembly 1 may be placed within a blood vessel at an area where an image is desired, i.e. the imaging environment (not shown). Turning to FIG. 1b, which shows a cross-sectional view of the imaging transducer assembly 1 of FIG. 1a from the distal end, the transducer assembly 1 then emits energy, via the PZT 40 and acoustic lens 30, in the form of acoustic beams 60 out of the sheath 5 and into the area being imaged. One of the purposes of the sheath 5 is to isolate the imaging transducer assembly 1 from the imaging environment yet maintain sonolucense so as to not distort the beams 60. These acoustic beams 60 reflect off targets in the area and then return to the transducer assembly 1. The received reflected beams 60 are then used to generate the desired image. The drive shaft 10 is used to steer and rotate the transducer assembly 1 within the sheath 5. By rotating the transducer assembly 1 by 360°, a complete cross-sectional image of the vessel may be obtained.
The quality of the image depends upon several factors. One of the factors is the width W of the acoustic beams 60. Accordingly, there is a need for an improved imaging device that outputs beams with a narrower width in order to increase the resolution of the image and allows images to be obtained for smaller objects.